Athletics teach you how to move smoothly and from your center. The modern study of athletic movement (as one would find in football, basket ball, track and field etc) teaches any of the things I can think of that are learned in "internal". The language is different but the lessons are the same. It's hard to go into anymore detail without further understanding your knowledge of sports training.

The internal power folks will tell you that the lessons aren't actually the same, that IP focuses on manipulating the structure of your own body, while athletes manipulate the outside world. They will also point out that internal strength continues to develop as people age, while athletic strength inevitably declines.

I do think that the degree of body control that some athletes have (notably gymnasts, but others as well) is often underestimated by non-athletes, but I'm not aware of any athletic discipline that claims to produce the abilities that the IP folks claim to have.

Studying the training of Chinese gymnasts and weightlifters might be interesting, as the Chinese seem fairly free of training dogma, and willing to consider any approach that works.